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February 2007

To Bee, or Not to Bee (with apologies to William Shakespeare)
Varroa Mite

Contact: Jerry Fischer, Maryland Department of Agriculture | 410-841-5920 | fischeje@mda.state.md.us

varroa mite
Photo: Stephen Ausmus, USDA Agricultural Research Service, www.forestryimages.org

(scroll to bottom for more images)

ANNAPOLIS, MD (February 1, 2007) - Honey bees, Apis mellifera, have a major role in the production of our food supply. In the U.S. they pollinate about 130 different crops with annual estimates of their pollination value alone, ranging from $5-14 billion; in Maryland, it has been valued at $40 million. Honey bees also produce honey, royal jelly and beeswax, which is widely used in cosmetics, lubricants and candles. Beekeeping, as a hobby, is enjoyed by thousands across the country.

Honey bees and beekeepers have long had to contend with predators like bears, skunks and insects, as well as diseases – foulbroods, chalkbrood, and nosema. The honey bee tracheal mite (Acarapis woodi), an internal parasite, literally suffocates bees, weakening colonies so much they may die, even with ample food present. A new threat, the varroa mite, is presently considered the single most serious enemy of honey bees in the U.S. For this reason, MISC has named it “Invader of the Month” for February.

The varroa mite, Varroa destructor (also sometimes called V. jacobsoni), originally described from Java, Indonesia, was first discovered in the U.S. in 1987, with detections in Wisconsin and Florida. In a very few years, it quickly spread throughout the U.S., and is now distributed worldwide. At present, in Maryland, it would be very difficult to find a honeybee colony without at least a few varroa mites. Varroa is an external parasite, brown, oval and flat, about 1 mm in size, that clings to its host with short, powerful legs, feeding on bee blood. Just imagine yourself walking around, covered with crawling bloodsucking frisbees©. This is life for an infested honeybee.

The female mite enters a brood cell containing a young bee larva and lays several eggs. After hatching, the young mites feed on the developing bee, which weakens, deforms, or sometimes kills it. The mature mites then seek out new cells for reproduction. The deformed bee, if it survives, may be unable to fly or assist in many hive duties. Piles of dead or crawling, deformed bees around the entrance are often signs of varroa infestation and colonies can die within a season or two.

Varroa mites actively search for drone (male) larval cells for egglaying. Drones, with their longer developmental time, allow for more mites to be produced per cell. Drones are also the most important dispersal method for mites, since they will be accepted at any colony, mites or no. Varroa mites are also spread by robber bees stealing honey from weakened, dead, or poorly defended colonies. Mites can hitch a ride to a new home.

By 1989, wild or feral colonies had virtually vanished from Maryland. The double attack of varroa and tracheal mites caused heavy losses; both commercial and hobby beekeepers scrambled to find safe miticides to use in their colonies. A few were approved, but in recent years, mites have developed resistance to some.

Fortunately, new weapons are available in the fight against varroa mites. One is the introduction of Russian bees that are more aggressive groomers and cleaners. These bees will go into infested cells and clean them out, as well as chew mites found on other adult bees. These behaviors lower mite populations, allowing the beekeeper to monitor mite populations and treat on an “as-needed” basis, thus slowing the development of resistance to chemical controls. A computer program “Varroapop”, (see links below) has been developed to help beekeepers predict treatment thresholds. In addition, research continues on both a fungus that kills varroa mites but doesn’t harm honey bees, and the use of essential oils and other chemicals to control mites in colonies.

Hobby beekeeping in Maryland has been negatively impacted. About one-third of new hobbyists leave beekeeping within 3 years because of varroa and the other problems that make it too difficult for a beginner, however, experienced beekeepers have been more able to adapt to the new enemy. As beekeepers are able to manage and maintain healthier colonies, feral colonies, formed by swarms, can again be found in the state, but these usually die within 2-3 years. So, small farm operations that used to rely on feral colonies for pollination, now must keep managed hives on site to ensure a good yield. These colonies are usually supplied by hobbyists on a cooperative basis.

The search continues for ways to protect this most valuable insect and “angel of agriculture”- the honey bee, alive, healthy, and productive.

For more information about other Invasive Species of Concern, visit www.mdinvasivesp.org or call the Maryland Department of Agriculture at 410-841-5920.

For more information on the Internet:

VarroaPop information

Fact Sheet. University of Florida, IFAS

Valuation of Pollination Services. Ecological Society of America

Managing Varroa Mites in Honey Bee Colonies (pdf). NC State University

Invasive.org

photos available electronically on request.

Varroa mite Varroa mite
Photos: Scott Bauer, USDA Agricultural Research Service, www.forestryimages.org

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